Structural member superior in water repellency and method for manufacturing the same

ABSTRACT

A structural member in which a super water-repellent function and high durability and scratch assistance can be obtained; and a method of manufacturing such a structural member. A water-repellent structure ( 100 ) consisting of appropriate irregularities comprising protrusion portions ( 18 ) uniform in height is formed on an external surface. The irregularities ( 17  and  18 ) have such dimensions that any droplet should not fall in a recess portion and the droplet is in contact with an air layer ( 20 ) in the recess portion ( 17 ).

TECHNICAL FIELD

The present invention relates to a structural member superior in waterrepellency for electric wires, building materials, ships, antennas, aircrafts, etc; and a method for manufacturing the same.

PRIOR ART

Water repellent treatment has been conventionally performed forpreventing adhesion of droplets or preventing pollution. Various waterrepellent materials and water repellent treatments have been developedand used in a variety of products including electronic equipment. Forexample, in order to obtain an electric wire to which snow hardlyadheres, JP-A-3-230420 proposes a method in which a carbon containingthin film is formed on the surface of an aluminum wire or the like, andthe film-formed wire is subsequently passed through a space where afluorine compound is ionized so that a fluorine compound thin film isformed on the wire. However, plasma polymerization of fluorine film isperformed in this method. Accordingly, the thin film may be easy to peeloff and inferior in adhesion. In addition, JP-A-3-84069, JP-A-4-258675and JP-A-2-238941 propose paints to be applied to ships, marine buildingmaterials, water transport pipes, etc. in order to prevent ice-adhesionor snow-adhesion or to prevent corrosion. However, there is a problemthat the paint is easy to peel off because the paint is applied in theform of a coating.

Further, JP-A-6-93121 proposes a method in which a surface of a basematerial is roughed by using FRP or the like as filler and achlorosilane surface active agent is absorbed in the roughed surface toperform water-repellent and oil-repellent treatment, in order to obtaina member which is superior in water repellency, oil repellency andantifouling property. In addition, JP-A-4-288349 proposes a techniquefor obtaining a water-repellent and oil-repellent film in which asurface is roughed by making a surface layer contain particulates or byapplying chemical etching to the surface, and a water-repellent polymerlayer is chemically bonded with the surface so as to form a film on thesurface. However, any technique disclosed in the above publications hasa problem that the film is uneven in height of the surface, insufficientin mechanical strength, problematical in durability and scratchresistance, and not uniform in water repellency. In addition,JP-A-10-156282 proposes a technique in which a water-repellent resinfilm of hydrophobic resin containing particulate powder is formed on asurface of metal material having a 0.1 to 50 μm fine irregularitystructure. However, this also has a problem that the film isinsufficient in mechanical strength and not uniform in water repellency.

Although those which have a water-repellent function are heretoforeproposed as mentioned above, each of the techniques has a problem indurability and scratch resistance, so that the water-repellent functioncannot be maintained over a long term.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a structural memberin which not only a super water-repellent function but also highdurability and high scratch resistance can be obtained; and to provide amethod for manufacturing such a structural member.

(1) A structural member according to an aspect of the present inventionis configured such that a water-repellent structure which is constitutedby appropriate irregularities of protrusion portions and recess portionsand which is uniform in height of the protrusion portions is formed onthe external surface of the structural member.

(2) A structural member according to the present invention is configuredsuch that in the above-mentioned structural member (1), the depth ofeach of the recess portions is not less than a predetermined value.

(3) A structural member according to another aspect of the presentinvention is configured such that in the above-mentioned structuralmember (1) or (2), the irregularities have a size enough to prevent adroplet from falling into a recess portion and to allow the droplet tocome into contact with an air layer in the recess portion.

(4) A structural member according to a further aspect of the presentinvention is configured such that in any one of the above-mentionedstructural members (1) to (3), a water-repellent film reactively bondedwith the irregularities of the water-repellent structure is formed onthe irregularities.

(5) A structural member according to a further aspect of the presentinvention is configured such that in any one of the above-mentionedstructural members (1) to (3), the water-repellent structure isconstituted by irregularities formed on a base material having awater-repellent function.

(6) A structural member according to a further aspect of the presentinvention is configured such that in any one of the above-mentionedstructural members (1) to (5), the irregularities comprises theprotrusion portions arranged in distribution in lines or in the form ofa lattice.

(7) A wire according to a further aspect of the present invention isconfigured such that a jacket of the wire is constituted by a structuralmember according to any one of the structural members (1) to (6).

(8) A building material according to a further aspect of the presentinvention is configured such that the building material has a surfacewhich is constituted by a structural member according to any one of thestructural members (1) to (6).

(9) A ship member according to a further aspect of the present inventionis configured such that the ship member has a surface constituted by astructural member according to any one of the structural members (1) to(6).

(10) An antenna according to a further aspect of the present inventionis configured such that the antenna has a surface constituted by astructural member according to any one of the structural members (1) to(6).

(11) An air-craft member according to a further aspect of the presentinvention is configured such that the air-craft member has a surfaceconstituted by a structural member according to any one of thestructural members (1) to (6).

(12) A method for manufacturing a structural member according to afurther aspect of the present invention is configured such that in amethod for manufacturing any one of the structural members (1) to (6),the irregularities of the water-repellent structure are formed by a moldhaving a shape corresponding to the irregularities.

(13) A method for manufacturing a structural member according to afurther aspect of the present invention is configured such that in themanufacturing method (12), a roller having an outer circumferentialportion in which the shape corresponding to the irregularities of thewater-repellent structure is formed is pressed onto the surface of abase material.

(14) A method for manufacturing a structural member according to afurther aspect of the present invention is configured such that in themanufacturing method (12), a not-yet-solidified base material is passedthrough a die having an inner circumferential portion in which the shapecorresponding to the irregularities of the water-repellent structure isformed.

(15) A method for manufacturing a structural member according to afurther aspect of the present invention is configured such that in themanufacturing method (14), the water-repellent structure is manufacturedby use of a photolithography method and an etching method. This etchingmethod is, for example, a trench dry etching method; an anodicelectrolysis method; an anisotropic wet etching method; an isotropic wetetching method; or an isotropic dry etching method.

In the present invention, a water-repellent structure in whichirregularities are formed in the outer surface and the protrusionportions of the irregularities are made uniform in height as mentionedabove to thereby obtain not only a super water-repellent function butalso high durability and high scratch resistance. That is, if theprotrusion portions are uneven in height as in the conventional case,portions in which a super water-repellent function cannot be obtainedare formed and the portions have an insufficient mechanical strength andeasily wear, so that there is a problem in durability and scratchresistance. However, in the present invention, such a problem is solved.In addition, when a water-repellent film is provided, thewater-repellent film is reactively bonded with the irregularities of thewater-repellent structure, so that the water-repellent film is hardlypeeled off. In addition, when the water-repellent structure ismanufactured by a photolithography method and an etching method in thepresent invention, it is possible to make the protrusion portionsuniform in height with precision. The details of the present inventionincluding its operation principle will be explained in Embodiment 1which will be described below. In the present invention, it is definedthat the conception of super water-repellency includes superoil-repellency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a water-repellent structure accordingto Embodiment 1 of the present invention;

FIG. 2 is an explanatory view of a contact angle of water when awater-repellent function is effected;

FIG. 3 is a view for explaining the dimensions of a recess portion and aprotrusion portion in FIG. 1;

FIGS. 4a-4 c are plan views of a water-repellent structure 100 in FIG.1;

FIGS. 5a-5 h are sectional views showing a manufacturing process forforming a water-repellent structure on a surface of a plate in amanufacturing method according to Embodiment 2 of the present invention;

FIG. 6 is a top view of the plate in which the water-repellent structurehas been formed on the surface;

FIGS. 7a-7 b are sectional views showing a manufacturing process of aplate in Comparison 1;

FIGS. 8a-8 b are sectional views showing a manufacturing process of aplate in Comparison 2;

FIGS. 9a-9 f are sectional views showing a manufacturing process forforming a water-repellent structure on a surface of a plate in amanufacturing method according to Embodiment 3 of the present invention;

FIGS. 10a-10 g are sectional views showing a manufacturing process forforming a water-repellent structure on a surface of a plate in amanufacturing method according to Embodiment 4 of the present invention;

FIGS. 11a-11 e are sectional views showing a manufacturing process forforming a water-repellent structure on a surface of a plate in amanufacturing method according to Embodiment 5 of the present invention;

FIGS. 12a-12 e are sectional views showing a manufacturing process forforming a water-repellent structure on a surface of a plate in amanufacturing method according to Embodiment 6 of the present invention;

FIG. 13 is a sectional view of a power line according to Embodiment 7 ofthe present invention;

FIGS. 14 and 15 are a perspective view and a front view, respectively,of a mechanism for embossing the circumference of the power line afterwire drawing to thereby form a water-repellent structure on the powerline;

FIGS. 16 and 17 are a sectional view of a mechanism for forming awater-repellent structure on the power line at the time of wire drawing,and a sectional view of a die thereof, respectively;

FIG. 18 is an explanatory view of a building material according toEmbodiment 8;

FIG. 19 is an explanatory view when a water-repellent structure isformed by embossing;

FIG. 20 is a sectional view of a ship according to Embodiment 9 of thepresent invention; and

FIG. 21 is a perspective view of an antenna according to Embodiment 10of the present invention.

THE BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIG. 1 is an explanatory view of a water-repellent structure accordingto Embodiment 1 of the present invention. In FIG. 1, in awater-repellent structure 100, recess portions 17 and protrusionportions 18 are formed on a surface of a silicon substrate 11, and awater-repellent film 19 is formed on the surfaces of the recess portions17 and the protrusion portions 18. Air layers 20 are generated in theserecess portions formed on the surface of the silicon substrate 11.Although this embodiment shows the case where the water-repellent film19 is formed, a base material which has a water-repellent function initself, for example, Teflon resin or the like may be used.

FIG. 2 is an explanatory view of a contact angle of water when thewater-repellent function is shown. To show the water-repellent function,it is necessary that the contact angle θ of water is 120 degrees or more(90 degrees or more in the case of an ink droplet) as shown in FIG. 2.In order to make the contact angle θ of water be 120 degrees or more sothat the water-repellent function is shown in the water-repellentstructure 100 in FIG. 1, it is preferable that the irregularities(recess-protrusion) have such dimensions as to prevent a droplet 21 fromfalling into a recess portion 17 and allow the droplet 21 to contact anair layer 20.

FIG. 3 is a view for explaining the dimensions of each recess portion 17and each protrusion portion 18 in FIG. 1. In FIG. 3, the symbol Adesignates a protrusion width (depending on mask design); B, a groovewidth (depending on the mask design); C, a working quantity (depth:depending on etching time); and D, a side wall angle (depending onetching condition). When this water-repellent structure is applied, forexample, to a structure which contacts with an ink droplet or the like,the above-mentioned widths A and B are restricted naturally by therelation with the diameter of the ink droplet, which is about 10 μm. Inaddition, the above-mentioned C needs to have a certain degree of depthfor preventing the ink droplet from getting in contact with the bottomof a groove and being enclosed therein. Therefore, the above-mentionedwidths A and B are restricted in a range from 0.2 to 500 μm, preferablyfrom 0.5 to 30 μm, more preferably from 1 to 10 μm. In addition, theabove-mentioned C is restricted to a depth of 1 μm or more, preferably 3μm or more, more preferably 5 μm or more. The evenness of the height ofthe protrusion portions is restricted to be within 0.5 times as large asthe value of the widths A and B, preferably within 0.3 times, morepreferably within 0.1 times, from the point of view of the scratchresistance.

FIG. 4 is a plan view of the water-repellent structure in FIG. 1. FIG.4(A) shows an example in which the protrusion portions 18 are arrangedand distributed regularly. FIG. 4(B) shows an example in which theprotrusion portions 18 are arranged in the form of lines. FIG. 4(C)shows an example in which the protrusion portions 18 are arranged in theform of a lattice. Although FIG. 4(A) shows an example in which theprotrusion portions 18 are square prisms, they may be various pillarssuch as triangular prisms, pentagonal prisms, hexagonal prisms, columns,etc.

Embodiment 2

FIG. 5 is a sectional view showing a manufacturing process for forming awater-repellent structure on a surface of a plate. FIG. 6 is a top viewof the plate 1 in which the water-repellent structure has been formed onthe surface. The procedure of manufacturing the water-repellentstructure will be described with reference to FIGS. 5 and 6. Here,description will be made about the case where the surface of a siliconsubstrate is worked by a photolithography method and a trench dryetching method so as to form a water-repellent structure.

{circle around (1)} First, a 4-inch single-crystal silicon wafer of the(100) crystal orientation is prepared as a base material of the plate 1.A silicon oxide film 12 of about 1,000 Angstroms is formed on at leastone surface of the single-crystal silicon substrate 11 by use of athermal oxidation method, as shown in FIG. 5(a).

{circle around (2)} Next, as shown in FIG. 5(b), about 2 ml ofphotosensitive resin OFPR-800 (viscosity: 30 cps) made by TOKYO OHKAKOGYO CO., LTD. is dropped onto the silicon oxide film 12 of thesingle-crystal silicon substrate 11, and spin-coated for 30 seconds atthe velocity of 5,000 rotations per minute, so that a photosensitiveresin film 13 is formed. By these spin-coat conditions, thephotosensitive resin can be applied so that the average film thicknessis about 1 μm with dispersion of 10% within the wafer surface.Incidentally, the coating film thickness may be changed appropriately inaccordance with the dimensions of a groove to be worked. The maximumvalue of the thickness of the photosensitive resin film to be applied is2 μm when the dimension of the groove width is 2 μm.

{circle around (3)} Next, the substrate 11 is dried for 30 minutes in anoven at a temperature of 90° C., and cooled down to the roomtemperature. As shown in FIG. 5(c), square protrusion-portion-expectedareas 13 each having one side in a range from 0.2 μm to 200 μm arephotolitho-patterned on the substrate 11. Then, the photosensitive resinis solidified by the oven at a temperature of 120° C., so that theetching-proof property is improved.

{circle around (4)} As shown in FIG. 5(d), the silicon oxide film ingroove-expected areas is etched with fluoric acid, and thephotosensitive resin is removed by release agent.

{circle around (5)} Next, by use of a trench dry etching apparatus, aplasma synthetic film 14 is formed with gas containing C and F, as shownin FIG. 5(e). Succeedingly, after the dry etching apparatus has beenevacuated, silicon in the area of groove bottoms 15 is etched withplasma of gas having a chemical formula SF6 or CF4, as shown in FIG.5(f). The above-mentioned plasma polymerization and plasma etching arerepeated. As a result, grooves each having the depth of about 5 μm areetched on the surface of the single-crystal silicon substrate 11 so thatthe recess portions 17 and the protrusion portions 18 are formed, asshown in FIG. 5(g). These protrusion portions 18 are laid out regularlyon the surface of the single-crystal silicon substrate 11, as shown inFIG. 6.

{circle around (6)} Next, fluoroalkylsilane or polyfluoroethylenewater-repellent material is deposited on the single-crystal siliconsubstrate 11 by a vacuum deposition method, so that a water-repellentfilm 19 is formed (FIG. 5(h)).

EXAMPLE 1

As Example 1 of the present invention, examples shown in Table 1 wereattempted in the above-mentioned Embodiment 2. First, substratematerials of samples 1 to 7 are prepared for the plate substrate 11.Then, the protrusion-portion-expected areas 13 (see FIG. 5(c)) areformed by patterning squares each in a range from 0.2 μm to 1,000 μm. Inaddition, the water-repellent film 19 on the plate 1 is formed bydepositing fluoroalkylsilane or polyfluoroethylene water-repellentmaterial. This water-repellent treatment is not performed on the samples2, 4 and 6.

TABLE 1 substrate protrusion size water-repellent material (micronsquare) treatment Sample 1 silicon 0.2 Yes Sample 2 silicon 0.2 NoSample 3 glass 5 Yes Sample 4 quartz 5 No Sample 5 quartz 10 Yes Sample6 silicon 10 No Sample 7 glass 500 Yes

(Comparison 1)

FIG. 7 is a sectional view showing a manufacturing process of Comparison1 in which water-repellent material is applied to a plate of stainlesssteel.

{circle around (1)} First, a substrate 31 is subjected to ultrasoniccleaning with an alkali solvent, as shown in FIG. 7(a).

{circle around (2)} The substrate 31 is immersed in nickel platingelectrolyte containing polyfluoroethylene particulates enhanced influorine atom density. Then, as shown in FIG. 7(b), an eutectoid platingfilm 33 in which polyfluoroethylene particulates 34 enhanced in fluorineatom density are dispersed is produced on the surface of the substrate31 by electric plating. This plating film 33 contains thepolyfluoroethylene particulates 34 enhanced in fluorine atom density.

(Comparison 2)

FIG. 8 is a sectional view showing a manufacturing process in thisComparison 2 in which a plate of polysulfone is coated withwater-repellent material.

{circle around (1)} First, a substrate 41 is subjected to ultrasoniccleaning with an alkali solvent, as shown in FIG. 8(a).

{circle around (2)} Succeedingly, the trade name “KANPENIREX”(fluorine-containing resin) made by KANSAI PAINT CO., LTD. is applied tothe surface of the substrate 41, so that a coating film 43 is producedas shown in FIG. 8(b).

Table 2 shows the results of measurement of contact angles of water tothe surfaces of the plates in the above-mentioned Example 1, Comparisons1 and 2.

TABLE 2 Water contact angle (degrees) Example Sample 1 160 Sample 2 150Sample 3 160 Sample 4 140 Sample 5 150 Sample 6 145 Sample 7 140Comparison 1 130 Comparison 2 160

As shown in the above Table 2, it was confirmed that each of the contactangles of water to the plates in this Example 1 (Samples 1 to 7)exceeded 120 degrees, which is higher than the value in Comparison 1.Further, through durability and scratch resistance tests, it wasconfirmed that this Example 1 (Samples 1 to 7) could obtain higherdurability and scratch resistance than Comparison 2.

EXAMPLE 2

In Example 2 of the present invention, examination was made about thecontact angle of water in the protrusion shapes of water-repellentstructures, which are arranged in square prisms, in lines and in theform of a lattice (see FIGS. 4(A), (B) and (C)). Table 3 shows data ofthem. It is understood that each of the water-repellent structures (No.1 to 10) according to the present invention had a contact angle of waterof 120 degrees or more so as to obtain a water-repellent function. AComparison of No. 11 in Table 4 in which a water-repellent film wasformed on a mirror-finished ground surface (correspondingly to the priorart), did not satisfy the necessary conditions for obtaining awater-repellent function.

TABLE 3 structure dimensions (actual measurements) protrusion grooveworking side wall pure width width quantity angle water No. structure A(μm) B (μm) C (μm) D (°) (°) 1 square 0.2 2.4 3.2 14 140 columns 2square 1.0 6.0 6.8 1 158 columns 3 lines 1.2 2.0 7.8 1 138 4 square 1.52.5 3.6 3 140 columns 5 square 3.4 3.8 5.0 12 140 columns 6 square 4.06.0 8.6 0 150 columns 7 lines 4.0 6.0 8.0 4 131 8 square 5.2 4.8 2.8 4149 columns 9 square 6.0 4.0 3.2 18 158 columns 10 lattice 4.3 6.0 10.02 123 11 comparative example: a water-repellent treatment onto 115 amirror surface

Embodiment 3

FIG. 9 is a sectional view showing another example of a manufacturingprocess for forming a water-repellent structure on a surface of a plate.Here, description will be made about the case where the surface of asilicon substrate is worked by a photolithography method and an anodicelectrolysis method so that a water-repellent structure is formed.

{circle around (1)} First, for example, a 200 μm thick n-typesingle-crystal silicon substrate 11 of the (100) crystal orientation isprepared as base material of a plate.

{circle around (2)} Silicon nitride films 23 and 24 0.3 μm thick areformed as etching-proof films on this silicon substrate 11 by a CVDapparatus, as shown in FIG. 9(a).

{circle around (3)} Next, after the silicon nitride film 24 is removedby a dry etching method, photo-etching is given to the silicon nitridefilm 23 so that the silicon nitride film 24 is etched in portions 22corresponding to the recess portions 17 of the water-repellentstructure, as shown in FIG. 9(b).

{circle around (4)} Next, etching pyramids 25 shaped into V-grooves areworked in the silicon substrate 11 by an anisotropic etching method witha potassium hydrate solution using the silicon nitride film 23 as amask. An indium-tin oxide film (ITO film) 26 is formed on the oppositesurface of the silicon substrate 11 to the surface where the siliconnitride film 23 has been formed as shown in FIG. 9(c).

{circle around (5)} Succeedingly, an electrolytic cell is so assembledthat the above-mentioned surface with the silicon nitride film 23 can bein contact with electrolyte. While light is irradiated to the siliconsubstrate 11 from the surface opposite to the surface with the siliconnitride film 23, grooves 27 about 5 μm deep are etched as shown in FIG.9(d), so that the recess portions 17 and the protrusion portions 18 areproduced (FIG. 9(e)).

{circle around (6)} Fluoroalkylsilane or polyfluoroethylenewater-repellent material is deposited on the plate by a vacuumdeposition method, so that a water-repellent film 19 is formed (FIG.9(f)).

Even in the above-mentioned water-repellent structure produced inEmbodiment 3, it was confirmed that a water-repellent function,durability and scratch resistance similar to those in theabove-mentioned Embodiment 2 could be obtained because of the evenheight of the protrusion portions.

Although examples using a silicon substrate as material of a plate aredescribed in the above-mentioned Embodiments 2 and 3, the material isnot limited to silicon material in the present invention. It is alsopossible to manufacture a plate of metal material such as stainlesssteel or a plate of organic polymeric material in the same manner asdescribed above. In that case, a similar function can be exhibited.

Embodiment 4

FIG. 10 is a sectional view showing a further example of a manufacturingprocess for forming a water-repellent structure on a surface of a plate.Here, description will be made about the case where a surface of asilicon substrate is worked by a photolithography method and ananisotropic wet etching method so as to form a water-repellentstructure.

{circle around (1)} First, a 4-inch single-crystal silicon wafer of the(100) crystal orientation is prepared as base material of a plate 1. Asilicon oxide film 112 having a thickness of about 1,000 Angstroms isformed on at least one surface of a single-crystal silicon substrate 111by use of a thermal oxidation method, as shown in FIG. 10(a).

{circle around (2)} Next, as shown in FIG. 10(b), about 2 ml ofphotosensitive resin OFPR-800 (viscosity: 30 cps) made by TOKYO OHKAKOGYO CO., LTD. is dropped onto the silicon oxide film 112 of thesingle-crystal silicon substrate 111, and spin-coated for 30 seconds atthe velocity of 5,000 rotations per minute, so as to form aphotosensitive resin film 113. By these spin-coat conditions, thephotosensitive resin can be applied so that the average film thicknessis about 1 μm with dispersion of 10% within the wafer surface.Incidentally, the coating thickness is changed appropriately inaccordance with the size of a groove to be worked. The maximum value ofthe thickness of the photosensitive material film to be applied is 2 μmwhen the size of the width of the groove is 2 μm.

{circle around (3)} Next, the substrate 111 is dried for 30 minutes inan oven at a temperature of 90° C., and cooled down to the roomtemperature. As shown in FIG. 10(c), protrusion-portion-expected areas113 which are 0.2 μm to 200 μm square are left on the substrate 111 byphotolitho-patterning. Then, the photosensitive resin is solidified bythe oven at a temperature of 120° C., so that the etching-proof propertyis improved.

{circle around (4)} As shown in FIG. 10(d), the silicon oxide film ingroove-expected areas is etched with fluoric acid, and thephotosensitive resin is removed by release agent.

{circle around (5)} Next, sectionally V-shaped etching pyramids 114 areformed in the silicon substrate 111 by an anisotropic etching methodwith a potassium hydrate solution using the silicon oxide film 112 as amask, as shown in FIG. 10(e). Then, the silicon oxide film 112 isremoved (FIG. 10(f)). These etching pyramids 114 formed thus correspondto the recess portions 17 in FIG. 1. Production of the recess portions17 results in formation of the recess portions 18 inevitably, so thatthe protrusion portions 18 are laid out regularly on the surface of thesingle crystal silicon substrate 111, as shown in FIG. 6.

{circle around (6)} Next, water-repellent material such asfluoroalkylsilaane or polyfluoroethylene is deposited on the plate by avacuum deposition method, so as to form a water-repellent film 19 (FIG.10(g)).

Embodiment 5

FIG. 11 is a sectional view showing a further example of a manufacturingprocess for forming a water-repellent structure on a surface of a plate.Here, description will be made about the case where a surface of asilicon substrate is worked by a photolithography method and anisotropic wet etching method so as to form a water-repellent structure.

{circle around (1)} First, a glass substrate 211, for example, 200 μmthick, is prepared as base material of a plate 1.

{circle around (2)} A silicon nitride film 212 having a thickness of 0.3μm is formed as etching-proof film on this glass substrate 211 by asputtering apparatus, as shown in FIG. 11 (a).

{circle around (3)} Next, photolitho-etching is given to the siliconnitride film 212 so that the silicon nitride film is etched in portionscorresponding to the recess portions 17 in the water-repellentstructure, as shown in FIG. 11(b).

{circle around (4)} Next, etching recess portions 215 are formed in theglass substrate 211 by an isotropic etching method with a hydrofluoricacid solution using the silicon nitride film 212 as a mask, as shown inFIG. 11(c).

{circle around (5)} Next, the silicon nitride film 212 is removed withhot phosphoric acid so that the irregularities are completed, as shownin FIG. 11(d).

{circle around (6)} Next, a fluoroalkylsilane film as a water-repellentfilm 19 is deposited on the plate by a vacuum deposition method (FIG.11(e)).

Embodiment 6

FIG. 12 is a sectional view showing a further example of a manufacturingprocess for forming a water-repellent structure on a surface of a plate.Here, description will be made about the case where the surface of asilicon substrate is worked by a photolithography method and anisotropic dry etching method so as to form a water-repellent structure.

{circle around (1)} First, a glass substrate 311, for example, 200 μmthick, is prepared as base material of a plate 1.

{circle around (2)} A photosensitive rein film 312 about 5 μm thick isformed as etching-proof film on this glass substrate 311 by a spin coatapparatus, as shown in FIG. 12(a).

{circle around (3)} Next, the photosensitive rein film 312 is etched inportions corresponding to the recess portions 17 in the water-repellentstructure by photolitho-etching, as shown in FIG. 12(b).

{circle around (4)} Next, etching recess portions 315 are worked in theglass substrate 311 by an isotropic plasma etching method with CF4 gasusing the photosensitive rein film 312 as a mask, as shown in FIG.11(c).

{circle around (5)} Next, the photosensitive rein film 312 is removedwith hot sulfuric acid so that the irregularities are completed, asshown in FIG. 11(d).

{circle around (6)} Next, a fluoroalkylsilane film as a water-repellentfilm 19 is deposited on the glass substrate 311 by a vacuum depositionmethod (FIG. 11(e)).

Even in the water-repellent structures produced in the above-mentionedEmbodiments 4 to 6, it was confirmed that a water-repellent function,durability and scratch resistance similar to those in theabove-mentioned Embodiment 2 could be obtained because of the evenheight of the protrusion portions.

In the above-mentioned Embodiments 2 to 6, a water-repellent structureis produced by a photolithography method and an etching method so that asurface of the base material can be replaced by the tops of protrusionportions. Accordingly, the protrusion portions inevitably become even inheight with precision.

Embodiment 7

FIG. 13 is a sectional view of a power line according to Embodiment 4 ofthe present invention. In this power line 50, a water-repellentstructure 52 is formed on the external surface of a sheath (vinyl) 51constituting a jacket of the power line 50. To form this water-repellentstructure 52, for example, the outer circumference of the sheath 51 isembossed after wire drawing, or grooves are formed at the time of wiredrawing.

FIGS. 14 and 15 are perspective and front views, respectively, of amechanism for embossing the outer circumference of the sheath 51 afterwire drawing so as to form the water-repellent structure 52 on the outersurface of the sheath 51. In this mechanism, a set of four rollers 53 ato 53 d and another set of four rollers 54 a to 54 d are disposed aroundthe power line 50 so as to be shifted from each other in thelongitudinal and circumferential directions of the power line 50. Anirregular portion (not shown) for forming the water-repellent structure52 on the external surface of the sheath (vinyl) 51 is provided on theexternal surface of each of the rollers 53 a to 53 d and 54 a to 54 d.In the state where the power line 50 is moved in the direction of theillustrated arrow, the rollers 53 a to 53 d and 54 a to 54 d rotatewhile embossing the power line 50 so that the water-repellent structure52 is formed all over the external surface of the sheath 51 of the powerline 50. Incidentally, the power line 50 may be moved by the rollers 53a to 53 d and 54 a to 54 d. Alternatively, the power line 50 may bemoved while being rotated.

FIG. 16 is an explanatory view showing a mechanism for forming groovesin the sheath 51 at the time of wire drawing. FIG. 17 is a sectionalview of a die of the mechanism. In wire drawing, vinyl 55 is coated byuse of a die 56 so that the sheath 51 is formed. At this time,irregularities 57 are formed in the inner wall of the die 56 in advanceas shown in FIG. 14 so that the water-repellent structure 52 is formedon the external surface of the sheath 51. The power line 50 may be drawnwhile being rotated.

Embodiment 8

FIG. 18 is an explanatory view of a building material according toEmbodiment 8 of the present invention. A water-repellent structure 61 isformed on the external surface of this building material 60. To formthis water-repellent structure 61, there are, for example, a method ofperforming a lithography method and an etching method which have beendescribed in Embodiments 2 to 6; a method of embossing the surface ofthe building material 60; and so on.

FIG. 19 is an explanatory view when the water-repellent structure 61 isformed by embossing. The building material 60 is, for example,constituted by a panel 62 and a thick coated film 63 formed on a surfaceof the panel 62. A pattern 64 in which irregularities have been formedis pressed to the coated film 63 before the coated film 63 is solidifiedso that the water-repellent structure 61 is formed. This pattern may bemanufactured, for example, by any manufacturing method according to theabove-mentioned Embodiments 2 to 6.

Embodiment 9

FIG. 20 is a sectional view of a ship according to Embodiment 9 of thepresent invention. A water-repellent structure which is similar to thatin the above-mentioned embodiments is formed on the external surfaces ofportions of this ship 70 which may come in contact with water, such as ahatch board 71; a hatch coaming 72; a deck plank 73; a hand rail 74; abulwark pole 75; a water way 76; a bulwark plate 77; a gunnel material78; a sheer-strake plate 79; a side panel 80; a wale 81; a bottom panel82; a garboard 83; a false keel 84; and so on. This water-repellentstructure is formed by pressing of the pattern 64 in FIG. 19 shaped intoa roll, or by pasting a film-like body formed according to any one ofthe above-mentioned Embodiments 2 to 6. For example, PTFE(polytetrafluorethylene) or silicon resin is used as this film-likebody.

Embodiment 10

FIG. 21 is a perspective view of an antenna (parabola) according toEmbodiment 10 of the present invention. A water-repellent structuresimilar to that in the above-mentioned Embodiments is formed on thesurface of this antenna 90. This water-repellent structure is formed bypressing of a pattern having irregularities which are similar to that inFIG. 19 and which correspond to the antenna, or by pasting a film-likebody formed according to any one of the above-mentioned Embodiments 2 to6.

Even in the above-mentioned Embodiments 7 to 10, the water-repellentstructure may be further subjected to a water-repellent treatment so asto form a water-repellent film.

In addition to the above mentioned embodiments, any portion which is aptto be easily damaged by adhesion of water or oil will be a target of thestructural members according to the present invention. For example,structural members according to the present invention may be used foroutside walls of airplanes. In that case, adhesion of ice and snow isprevented, so that the safety and fuel economy of the airplanes areimproved.

What is claimed is:
 1. A structural member formed of a single crystalsilicon substrate, comprising: a water-repellent structure formed on anexternal surface of said structural member, said water repellentstructure is constituted by irregularities of protrusion portions andrecess portions and said protrusion portions are substantially uniformin height and shaped as prisms, wherein said protrusions have a topsurface width in a range of 1 to 10 μm and said recesses have an upperopening width in a range of 1 to 10 μm, so that any droplet minimallyfalls in any of said recess portions and each droplet comes into contactwith an air layer in each of said recess portions.
 2. The structuralmember according to claim 1, wherein each of said recess portions has adepth of about 5 μm.
 3. The structural member according to claim 1,wherein a water-repellant film reactively bonded with saidirregularities of said water-repellent structure is formed on saidirregularities.
 4. The structural member according to claim 1 whereinsaid prisms further comprise at least one of the group selected fromsquare prisms, triangular prisms, pentagonal prisms and hexagonalprisms.
 5. The structural member according to claim 1, wherein each ofsaid recess portions has a depth of about 3 μm.
 6. The structural memberaccording to claim 1, wherein each of said recess portions has a depthof about 1 μm.
 7. The structural member according to claim 1 whereinsaid protrusion portions have an evenness of height which is within 0.1times a width of one of the group selected from the protrusion portionsand the recess portions.
 8. The structural member according to claim 7,wherein each of said recess portions has a depth of about 5 μm.
 9. Thestructural member according to claim 7, wherein each of said recessportions has a depth of about 3 μm.
 10. The structural member accordingto claim 7, wherein each of said recess portions has a depth of about 1μm.
 11. The structural member according to claim 7, wherein said prismsfurther comprise at least one of the group selected from square prisms,triangular prisms, pentagonal prisms and hexagonal prisms.
 12. Thestructural member according to claim 1 wherein said protrusion portionshave an evenness of height which is within 0.3 times a width of one ofthe group selected from the protrusion portions and the recess portions.13. The structural member according to claim 1 wherein said protrusionportions have an evenness of height which is within 0.5 times a width ofone of the group selected from the protrusion portions and the recessportions.
 14. A structural member formed of a single crystal siliconsubstrate comprising: a water-repellent structure formed on an externalsurface of said structural member, said water repellent structure isconstituted by irregularities of protrusion portions and recess portionsand said protrusion portions are substantially uniform in height with anevenness of height which is within 0.5 times a width of one of the groupselected from the protrusion portions and the recess portions whereinsaid protrusions have a top surface width in a range of 1 to 10 μm andsaid recesses have an upper opening width in a range of 1 to 10 μm, sothat any droplet minimally falls in any of said recess portions and eachdroplet comes into contact with an air layer in each of said recessportions.
 15. The structural member according to claim 14, wherein saidirregularities comprises the protrusions arranged in one of adistribution, in lines, and in a lattice.